1. Field of the Invention
The present invention relates to novel N-substituted peptidyl compounds represented by the general formula (1) to be noted hereinafter. The present invention also relates to a cysteine proteinase inhibitor that contains a compound of the general formula (1) as an active ingredient and which shows strong enzyme inhibitory activity toward cysteine proteinases, in particular papain, calpain and even cathepsin.
2. Prior Art
Drugs that specifically inhibit the activity of papain (E.C. 3.4.22.2) and calpain (E.C. 3.4.22.17), which are both cysteine proteinases, have the potential to be used as anti-inflammatories, so there has been a definite need for the development of such drugs. Calpain occurs extensively in mammals and birds and the predominant site of their presence is cytosol. Abnormal activation of this enzyme is con-sidered to be responsible for the development of muscular dystrophy and cataracts. Cathepsin (E.C. 3.4.22.1) is a proteinase that is localized in lysosome and its abnormal activation seems to be responsible for cancer metastasis and for the development of muscular atrophy and muscular dystrophy. Hence, drugs that specifically inhibit the activity of calpain or cathepsin are desired for the purpose of developing therapeutic agents for muscular dystrophy, muscular atrophy and cataracts, as well as drugs capable of inhibiting cancer metastasis. As adjuncts to the efforts being made to develop these drugs, various cysteine proteinase inhibiting substances have been discovered (Shimizu, B. et al., J. Antibiot., 25, 515, 1972, Japanese Patent Public Disclosure Nos. 60-28990, 61-106600 and 61-103897). However, the inhibitors that have been known so far still leave room for improvement with respect to activity and transferrability into the body. Hence a particularly great need exists for the development of compounds that have a strong capability to inhibit cysteine proteinases including papain, calpain and cathepsin.